Borrasca (1962)

Sam Walker moves to the town of Drisking, Missouri one summer and quickly befriends two other kids, Kyle and Kimber. When Sam's sister, Whitney, disappears a few months later, he passes five lonely years wondering what happened to her. When more people start disappearing suddenly, the three take it upon themselves to find out what's happening to all the disappearing people and what connection the disappearances hold with the mountain outside of town.